24-08-2015, 08:18 AM
Drifting temporarily off topic...
Intermediate frequencies varied from make to make, and often had changes for certain locations to overcome heterodynes.
But modern AM sets (if you can still buy them!) standardised on 455 kHz across the globe.
455 x 2 = 910. When Radio Five started on 909, there were listener complaints about a 'tunable whistle'. Presumably because the station was very widely listened to on a variety of sets.
The joggling onto 9kHz spacing on MW (actually all multiples of 9, e.g. 891, 900 kHz, 909, etc.) was intended to not only make synthesized set design easier, but to get the few European stations to get onto the correct channel; there always had been a few that had odd 1 kHz offsets to the main channel causing hets. It took some months to get a few Portuguese and North African stations on the right channel - where they'd never bothered before. Then there was (and still is?) Albania on approximately 1215 kHz!
The MW shifts were done almost entirely over one night, but LW took longer, done in two or three stages - I can't remember now. Although there are fewer LW stations, they usually run more power, and a 1 or 2 kHz shift is a lot to adjust the antenna for at these frequencies!
There is an inconstancy to the LW 9 kHz spacing; two stations on either side of the old East/West German border had to split a channel. That's why digital long-wave tuners don't jump in 9 kHz steps. I'm sure someone can come up with the names and locations of these two stations, but I expect one if not both of them have now closed.
Then there's the whole area of what frequency accuracy is necessary, internationally and domestic synchronised groups like 693, 909, etc. But that's drifting way off topic...
Ian
Intermediate frequencies varied from make to make, and often had changes for certain locations to overcome heterodynes.
But modern AM sets (if you can still buy them!) standardised on 455 kHz across the globe.
455 x 2 = 910. When Radio Five started on 909, there were listener complaints about a 'tunable whistle'. Presumably because the station was very widely listened to on a variety of sets.
The joggling onto 9kHz spacing on MW (actually all multiples of 9, e.g. 891, 900 kHz, 909, etc.) was intended to not only make synthesized set design easier, but to get the few European stations to get onto the correct channel; there always had been a few that had odd 1 kHz offsets to the main channel causing hets. It took some months to get a few Portuguese and North African stations on the right channel - where they'd never bothered before. Then there was (and still is?) Albania on approximately 1215 kHz!
The MW shifts were done almost entirely over one night, but LW took longer, done in two or three stages - I can't remember now. Although there are fewer LW stations, they usually run more power, and a 1 or 2 kHz shift is a lot to adjust the antenna for at these frequencies!
There is an inconstancy to the LW 9 kHz spacing; two stations on either side of the old East/West German border had to split a channel. That's why digital long-wave tuners don't jump in 9 kHz steps. I'm sure someone can come up with the names and locations of these two stations, but I expect one if not both of them have now closed.
Then there's the whole area of what frequency accuracy is necessary, internationally and domestic synchronised groups like 693, 909, etc. But that's drifting way off topic...
Ian
